The mitochondrial control region reveals genetic structure in southern kingcroaker populations on the coast of the Southwestern Atlantic

Abstract

The western portion of the Atlantic Ocean exhibits different hydrographic, geomorphological and climatic characteristics which may interfere with the genetic structure of fish species inhabiting coastal waters. Studies of mitochondrial DNA indicate that species with a broad geographic distribution tend to exhibit some degree of genetic structure. Menticirrhus americanus was thus chosen as the subject of the present study, given that it has a very ample distribution and it is an estuarine-dependent species. In the present study, sequences of the mtDNA Control Region were analyzed in 224 individuals from 11 localities on the Atlantic coast of South America. The results revealed the presence of three distinct population groups: group I (northern and northeastern Brazil), group II (southern and southeastern Brazil), and group III (Uruguay). Sixteen of the 113 haplotypes were found exclusively in the Uruguayan populations, 67 were observed only in group I, and 27 were exclusive to group II. There is thus an absolute separation of the populations of M. americanus from Uruguay and Brazil, while little genetic structuring was found in the Brazilian populations. The phylogeographic pattern observed in M. americanus may be accounted for the existence of at least two barriers to gene flow. One corresponds to the Vitória-Trindade seamount (in Espírito Santo), while the other is found further south in the region of the River Plate, separating the populations from Brazil and Uruguay apparently because of the convergence zone between the Brazilian and Malvinas Currents. The results of this study corroborate previous research, which shows that ecological patterns, combined with the geomorphology and hydrodynamics of the southwestern Atlantic, influence the genetic structure of local fish populations. Therefore, effective fishery managements should be taken to assure a sustainable exploitation of southern populations avoiding losses of diversity and resilience to environmental fluctuations.